1. Technical Field of the Invention
The present invention relates generally to a method and system for applying a liquid, which contains a resin or the like dissolved in a solvent, e.g., a polyimide solution, on a substrate, such as a semiconductor wafer or an LCD substrate (a glass substrate for a liquid crystal display), to form a liquid film.
2. Description of Related Art
As one of semiconductor fabricating steps, there is a process for applying a polyimide on a substrate, such as a semiconductor wafer, in order to form a protective film or interlayer insulating film of a semiconductor device. In such a process, it is conventionally required that the thickness of a coating film formed on the surface of the substrate is uniform over the whole. In recent years, with the scale down of circuits and so forth, it is required that the inplane uniformity of the thickness of the film is higher than that of conventional films.
In the circumstance, as one of coating film forming systems, there has been studied a system for further diluting a chemical, which contains a polyimide dissolved in a solvent, to prepare a coating liquid and for rotating a semiconductor wafer (which will be hereinafter referred to as a wafer) as shown in, e.g., FIG. 11, to discharge the coating liquid 12 from a nozzle 11 onto the surface of the wafer W while gradually moving the nozzle 11 in a radial direction from the center of the wafer W, to spirally apply the coating liquid 12 in the same manner as a picture drawn with a single stroke of the brush.
In such a system, the lines of the spirally coating liquid are tightly arranged without providing gaps in radial directions of the wafer W to integrate the lines of the coating liquid, so that a coating film having a high inplane uniformity of thickness is formed. Specifically, for example, coating data including values, such as the rate of discharge of the coating liquid, the speed of rotation of the substrate, and the traveling speed of the nozzle, are prepared on the basis of previously measured data, and the coating liquid is applied on the basis of this data.
However, since the above described system uses a nozzle having a small diameter of, e.g., about 100 xcexcm, cavitation occurs in the passage of the nozzle, and bubbles of the coating liquid generated by the cavitation are broken on the surface of the wafer W, so that there is a problem in that an uncoated region formed by breaking the lines of the coating liquid is generated. For that reason, for example, various measures to provide a degassing mechanism upstream of the nozzle for removing bubbles remaining in the coating liquid have been studied. However, the effects of all of the measures are insufficient.
Using a small-diameter nozzle, the width of the lines of the coating liquid applied on the wafer W is decreased. In order to tightly arrange such thin lines of the coating liquid, the nozzle must be very precisely moved with respect to the wafer W on the basis of the above described coating data. However, although the coating data have a predetermined error range every condition, if all values of the above described three conditions, e.g., the rate of discharge of the coating liquid, the speed of rotation of the substrate and the traveling speed of the nozzle, are values approximating the limit of error, the adjacent lines of the coating liquid are partially spaced from each other, so that there are some cases where a linear uncoated region is generated in each gap.
Moreover, although the coating liquid is applied so as to apparently draw a spiral, the nozzle does not spirally move in fact, and the position of the nozzle is changed by the balance between the rotation of the wafer W and the straight-line motion of the nozzle in radial directions of the wafer W. Therefore, the coating liquid on the wafer W varies slightly step-wise from a microscopic point of view, and if this step increases, a linear uncoated region is generated between the adjacent lines of the coating liquid.
The present invention has been made on the basis of the circumstances, and it is an object of the present invention to provide a technique for enhancing the inplane uniformity of the thickness of a coating film to improve throughput when the coating film is formed on a substrate.
A coating film forming method according to the present invention comprises: a first coating step of moving a nozzle, which is provided above a substrate, from the center of rotation of the substrate toward a peripheral edge of the substrate and discharging a coating liquid containing a coating film component and a solvent, while rotating the substrate horizontally held, to spirally apply the coating liquid to form a coating film on the substrate; a monitoring step of monitoring the state of the surface of the substrate in a coated region to detect an uncoated region generated in the coated region in which the coating liquid is applied by the nozzle at the first coating step; and a second coating step of applying the coating liquid so as to fill the uncoated region with the coating liquid by the nozzle when the uncoated region is detected at the monitoring step.
According to such a method, it is possible to surely fill the coating liquid in the uncoated region which is easily generated when the coating liquid is spirally applied, so that it is possible to enhance the inplane uniformity of the thickness of the coating film. Specifically, separate nozzles are preferably prepared for the first and second coating steps, and the monitoring step is preferably a step of monitoring the surface of the substrate in the vicinity of a position just below the nozzles. Thus, when the uncoated region is detected, it is possible to carry out the second coating step without waiting the end of the first coating step, so that it is possible to improve throughput.
The monitoring step is preferably a method for detecting the uncoated region by irradiating the surface of the substrate with light and monitoring the intensity of reflected light, or a method for detecting the uncoated region by monitoring a difference in level on the surface of the coating liquid which is applied on the substrate.
According to the present invention, the first coating step may be a step carried out on the basis of coating data including a rotation-speed pattern indicative of the relationship between the position of the nozzle and the speed of rotation of the substrate at that position, and a traveling pattern indicative of the relationship between the position of the nozzle and the traveling speed of the nozzle at that position, and the coating film forming method may include a data modifying step of modifying the coating data so as not to generate the uncoated region at the same place when the uncoated region is detected at the monitoring step. This data modifying step is preferably a step of determining that the setting of the coating data is erroneous when the uncoated region is continuously detected two times at the same place of a plurality of substrates at the monitoring step, and modifying a rotation pattern so that the speed of rotation of the substrate increases during the whole time in which the coating liquid is applied, when it is determined that the coating data is erroneous. In addition, the coating data modified at the data modifying step changes in accordance with a position on the substrate at which the uncoated region is detected.
A coating film forming system according to the present invention comprises: a substrate holding portion for horizontally holding and rotating a substrate; a main nozzle for spirally applying a coating liquid containing a component of a coating film and a solvent on the surface of the substrate to form the coating film thereon, the main nozzle moving between a central portion and outer edge portion of the substrate held on the substrate holding portion; monitoring means for monitoring the state of the surface of the substrate in a coated region to detect an uncoated region generated in the coated region in which the coating liquid is applied by the main nozzle; and an auxiliary nozzle for applying the coating liquid so as to fill the uncoated region with the coating liquid when the monitoring means detects the uncoated region generated in the coated region.
With such a construction, the main nozzle is preferably formed so as to integrally move with the monitoring means.
The coating film forming system may further comprise data modifying means for modifying coating data on the basis of the coating data including a rotation-speed pattern indicative of the relationship between the position of the first nozzle and the speed of rotation of the substrate when the first nozzle exists at that position, and a traveling pattern indicative of the relationship between the position of the first nozzle and the traveling speed of the first nozzle at that position, so as not to generate the uncoated region at the same place when the uncoated region is detected by the monitoring means.